In Favor of Controlling Proven, but Not Probable, Causes of Cancer
We wish to compliment and comp lement the editorial by Landrigan et al. (2 011) who inter alia synthesized the "Asturias Declaration" d u ring the "International Conference on Environmental and Occupational Determinants of Cancer: Interventions for Primary Prevention" [World Health Otganization (WHO) 2011 ]. Although the authors list recommendations that are certainly commendable, we strongly disagree with the inclusion of "probable" in the suggestion that "the WHO should develop a global framework for control of environmental and occupational carcinogens that concentrates on the exposures identified by lARC [International Agency for Research on Cancer] as proven or probable causes of human cancer."
Indeed, we would strongly suggest t he need to focus on the causes of human cancer that have been identified by IARC as proven, but not o n "probable" causes [59 agents have been classified by IARC as group 2A, i.e., probably carcinogenic to humans (TARC 201 1)] to then direct premature prevention efforts on the latter. Soberingly, IARC s diligent evaluation process of what can and what can not cause cancer in human s would be blurred when equating group 1 (proven carcinogen) classifications with group 2A classifications, as recommended in the Asturias Declaration. A group 2A classification is not necessarily part of a one-way street to a group 1 verdict.
To provide a recent, empirical example, shift-work that involves circadian disruption was classified as a probable human carcinogen (Srraifera1. 2007). Importantly, though, as long as causality is not established, we should clearly be deterred from activities that are not driven by data. Moreover, means for primary prevent ion are elusive (Erren et al. 200 9): Shift-work is unavoidable in our 24/7 societies, and it is impossible with today's stat e of knowledge to identify workers who are robust to shift-work conditions and to dissuade others who may be susceptible to the effects of circadian disrupt ion or chronodisruption (Erren et al. 20 08; Erren and Reiter 2008). An lARC classification of "probable " human carcinogen, which implies uncertainty and the possibility that future research may exonerate the "culprit in question, " is certainly not an appropriate yardstick to guide valuable and limited resources. Instead, we should invest in controlling established carcinogens such as asbestos and smoking.
Overall, when Richard Nixon declared the war on cancer on 23 December 1971, he remarked, "I hope in the year s ahead that we may look back on this day and this action as being the most significant action taken during this ad ministration" (Nixon 197 1b). That initiative certainly is no t-not only because of the Watergate scandal but, importantly, because of t he highly ambitious goal "to find a cure for cancer" (Nixon 197 1a). Lacking insights in to how to cure cancer in the majority of cases, our objective for now-and presumably for many years to come-should be improved primary prevention of environmentally and occupationally caused cancers. …